The disclosure relates to a hydrostatic pressure flow control device particularly adapted for an above ground or below ground holding pond (generally referred to as a pond) that is adapted to collect storm water where the flow control device is in fluid communication therewith. The general purpose of the pond is to prevent a large influx of water into a nearby stream or the like which can potentially cause environmental damage. Many regulations require storm water and other runoff water to be directed into a holding pond and then discharged at an adequate flow rate to meet regulated criteria.
In an urban development where forest is removed and is replaced with items such as concrete and the like which have distinctly different runoff characteristics, a detention pond must be implemented for handling storm water. In general, there are two things which must occur with storm water: it must be cleaned, and it must be metered. In one preferred form, there is bioswale that is positioned between a control structure and a main pond volume. In low flows, the bioswale acts as a filtering device, whereby water passes therethrough due to gravitational flow to the control structure. In high flows, the control tower essentially backs up the flow, thereby filling the bioswale and the main large tank. In the control structure there is generally an orifice in the upper portion that is adapted to have the water pass therethrough in a “design H” situation which is essentially a two-year flood, whereby the maximum amount of allotted throughput of water, by the local environmental standards, passes therethrough. Of course, this does not occur until the water level is quite high, and the entire pond is filled up to the upper portions and the maximum capacity thereof.
Generally, state and Federal Departments of Ecology are concerned with fluid throughput between various creek beds and the like, so ecological systems such as salmon eggs are not washed out during a deluge or any form of rain or flood. Essentially, the detention pond is adapted to mimic the pre-developed condition, whereby the dampening effect by the inherent capacitance of all of the forest and under brush. Development such as rooftops, parking lots and other hard surfaces decrease an area's water capacitance. Therefore, the natural flow control is effectively reproduced by the pond and a flow metering device.
It should be noted that there are three essential flow durations (rates over a set period of time) that are allowed: 50% of the two-year flood, 100% of the ten-year flood, and 100% of the hundred-year flood throughputs. These amounts are flow durations, which are measured in cubic feet per second multiplied by number of hours.
Therefore, it is advantageous to have a maximum allowable throughput during the various height conditions of the pond. In one form, this is accomplished by having a fixed hydrostatic head with a known orifice where the head will stay constant regardless of the water level as shown in the detailed description below. In one form, this head is 49% of a two-year amount, which is the maximum allotted throughput amount as per the Department of Ecology standards (at the present time of filing in the Inventor's state of residence which is Washington State).
Therefore, it is extremely advantageous to have a controlled higher throughput of fluid so that the backup of water in the settling pond is a lesser net volume. This allows for a greater amount of real estate to be utilized for other, more usable land or preserved land in the pre-developed state.
The apparatus as described further below functions as an early release mechanism. In the northwest region of the United States, a thirteen-acre developed site would normally require a 41,400 square foot sized pond with prior-art flow control systems in place. With the invention as described below in place, the pond is essentially reduced in topographical square feet by 38%. It should be noted that given the angle of repose of the soil, there is a fixed amount of depth and volume that can occur given a certain square-footage of allotted space for a pond. Additionally, in some embodiments the items are submerged in a concrete box beneath usable soil; however, this is an expensive installation, and of course, reducing the overall size is potentially advantageous.
With regard to the above example that was in use, the implementation of the invention would save approximately $75,000 in estimated costs using the flow control system as claimed.
In the Civil Engineering pond design and installation disciplines, there is psychological trend to guard against the maximum flow and not be concerned with the flow rates that occur immediately leading up thereto. In other words, the prior art is concerned with the maximum flow rates where the damage can occur and not exceeding these flow rates; however, this line of thinking has a tendency to neglect the flow rates immediately preceding and leading up the maximum allowable flow rate. A system as described below provides a maximum allowable flow rate as soon as possible to increase the net volume passing through the pond and the system hence allowing a smaller volume pond to be in place.